The present invention relates to a railroad track maintenance vehicle and associated method for measuring and maintaining the level of a railroad track.
Trains and other rail vehicles exert tremendous forces on a track when passing thereover. These forces cause movement of the track within the flexible stone bed. Settling and degradation of the ballast stones in the track bed result in deterioration of track level and alignment, which can increase the likelihood of train derailment. Accordingly, periodic reconditioning of the track bed is necessary to maintain the track in a safe condition.
One conventional technique for reconditioning the railroad track bed is known as tamping. Tamping involves lifting the railroad rail and ties and redistributing the existing ballast stones under the lifted tiles to place the rail back into level. A second known technique for reconditioning a railroad track bed is referred to as stoneblowing. Stoneblowing involves lifting the railroad rail and ties and blowing new ballast stones under the lifted ties. In either technique, it is necessary to measure the track level prior to "working" the track to determine where lifting is needed.
Several devices for measuring track level have been developed. A first device includes a pair of chords, one stretched over each of the track rails. A number of transducers are positioned at locations along each chord to measure the distance between the taut chord and the rail. Each transducer measures the deviation of the rail from the straight line defined by the end points of the chord at each measuring position. Measurements are taken at sufficient positions to allow the generation of both loaded and unloaded profiles. Each transducer includes a trolley having a measuring arm that extends upward and is affixed to the chord. As the track rails: rise and fall, the measuring arm, which follows the chord, moves in relation to the trolley to generate an analog signal corresponding to the rise and fall of the rails. The signals are stored and used to reconstruct a mathematical model of the measured track, which can be used in working the track. It should also be noted that the physical chords can be replaced by light beams and optical followers.
A further system is used to measure the crossfall of the rails. Crossfall refers to the transverse level between the two rails. One particular method of measuring crossfall accurately at speed combines measurements of crossfall from different sources, each having particular advantages and disadvantages. The short wavelength crossfall for any location along the rails may be accurately measured by comparing the profile of the first rail at that location with the measured profile of the second rail at that same location. The long wavelength crossfall measurement may be accurately obtained by filtering the output of an inclinometer that is towed along the rails by the track maintenance vehicle. The acquired data is processed to provide a complete profile of the track. The chord type system is subject to error under a variety of circumstances, such as; incorrect trolley deployment, varying chord tension, transducer friction or failure, and profile reconstruction software error. In addition, the systems described suffer from mathematical shortcomings such as "blind spots" where harmonic wavelengths of the transducer/chord distances cannot be measured.
A second method for measuring both longitudinal level and crossfall uses a device commonly referred to as a "frog." A frog includes two gravity sensing inclinometers mounted on a trolley or handcart that is pushed by hand or towed by a vehicle along the rails. The first inclinometer is mounted in alignment with the length of the track and measures the rise and fall of the rails. The second inclinometer is mounted transverse to the length of the track and measures the crossfall of the rails. The inclinometers are affected by acceleration forces and therefore require a small "rest period," or setting time, prior to each measurement. Accordingly, the frog must travel intermittently along the rails, requiring stationary positioning at each measured location, to provide the necessary rest period. It is this intermittent motion that earns this device its name, "frog."
An interconnected towing vehicle and frog are disclosed in United Kingdom Patent No. 2,085,825 published May 6, 1982, and owned by the British Railways Board. The frog is connected to and driven by the towing vehicle in a "lost motion" linkage. The lost motion technique provides; intermittent movement of the frog while the towing vehicle moves continually, thereby establishing a rest period during which the gravity sensing inclinometers settle prior to each measurement. To work the track, the towing vehicle and frog traverse the track in a first pass; the data is analyzed; and then the maintenance vehicle makes a separate pass over the track.
In addition, like the chord type measuring system, frog type measuring systems are subject to a variety of failures that may lead to inaccurate profile reconstruction.